1. Field
The present disclosure relates to an amplifier circuit, and more particularly, to a capacitive trans-impedance amplifier circuit implemented as a part of a pixel architecture and interfacing with a sensing device such as a photodetector.
2. Description of the Related Art
Capacitive Trans-Impedance Amplifier (CTIA) circuits have been utilized in a variety of applications, for example, in pixel architectures for use with photodetectors. A CTIA circuit converts an input photocurrent or photocharge (for example, from infrared radiation) into an output voltage. The charge-to-voltage conversion gain (usually expressed in microvolts per electron) is determined by the CTIA feedback capacitance. For low levels of infrared radiation and in order to achieve low input-referred noise, the conversion gain needs to be high, which in turn means that the CTIA feedback capacitance needs to be small (e.g., less than 2 femtofarads). In such a scenario, the charge injected by the MOS reset transistor at the CTIA input at the end of the reset phase (when the MOS reset transistor turns off) leads to a large voltage error at the CTIA output. This voltage error significantly reduces the available voltage swing at the CTIA output.
There is a need in the art for a CTIA circuit that can effectively compensate the charge injected by the MOS reset transistor at the CTIA input when the MOS reset transistor turns off. It should also be recognized that the injected charge is subject to variability because it depends on a number of factors such as the slope of the reset clock signal and the impedance at the CTIA input and output. Therefore, there is a need in the art for a CTIA circuit that enables control of, and adjustability in, the amount of charge compensation. It is desirable for the elements of the CTIA circuit to be implemented over a relatively small layout area. It is further desirable to have the ability to compensate small amounts of charge (less than the channel charge of a minimum-sized MOS transistor) and to have uniform charge compensation across the pixel array.